glConvolutionFilter2D builds a two-dimensional convolution filter
kernel from an array of pixels.

The pixel array specified by width, height,
format, type, and image is extracted from memory and processed just as
if glDrawPixels were called, but processing stops after the final expansion
to RGBA is completed.

The R, G, B, and A components of each pixel are next
scaled by the four 2D GL_CONVOLUTION_FILTER_SCALE parameters and biased
by the four 2D GL_CONVOLUTION_FILTER_BIAS parameters. (The scale and bias
parameters are set by glConvolutionParameter using the GL_CONVOLUTION_2D
target and the names GL_CONVOLUTION_FILTER_SCALE and GL_CONVOLUTION_FILTER_BIAS.
The parameters themselves are vectors of four values that are applied to
red, green, blue, and alpha, in that order.) The R, G, B, and A values are
not clamped to [0,1] at any time during this process.

Each pixel is then
converted to the internal specified by internalformat. This conversion
simply maps the component values of the pixel (R, G, B, and A) to the values
included in the internal (red, green, blue, alpha, luminance, and intensity).
The mapping is as follows:

Internal Format Red Green Blue Alpha Luminance Intensity

GL_ALPHA A

GL_LUMINANCE R

GL_LUMINANCE_ALPHA A R

GL_INTENSITY R

GL_RGB R G B

GL_RGBA R G B A

The red, green, blue, alpha, luminance, and/or intensity components of
the resulting pixels are stored in floating-point rather than integer They
form a two-dimensional filter kernel image indexed with coordinates i and
j such that i starts at zero and increases from left to right, and j starts
at zero and increases from bottom to top. Kernel location i,j is derived
from the Nth pixel, where N is i+j*width.

Note that after a convolution
is performed, the resulting color components are also scaled by their corresponding
GL_POST_CONVOLUTION_c_SCALE parameters and biased by their corresponding
GL_POST_CONVOLUTION_c_BIAS parameters (where c takes on the values RED,
GREEN, BLUE, and ALPHA). These parameters are set by glPixelTransfer.

GL_INVALID_ENUM is generated if internalformat
is not one of the allowable values.

GL_INVALID_VALUE is generated if width
is less than zero or greater than the maximum supported value. This value
may be queried with glGetConvolutionParameter using target GL_CONVOLUTION_2D
and name GL_MAX_CONVOLUTION_WIDTH.

GL_INVALID_VALUE is generated if height
is less than zero or greater than the maximum supported value. This value
may be queried with glGetConvolutionParameter using target GL_CONVOLUTION_2D
and name GL_MAX_CONVOLUTION_HEIGHT.

GL_INVALID_ENUM is generated if format
is not one of the allowable values.

GL_INVALID_ENUM is generated if type
is not one of the allowable values.

GL_INVALID_OPERATION is generated if
glConvolutionFilter2D is executed between the execution of glBegin and
the corresponding execution of glEnd.

GL_INVALID_OPERATION is generated
if height is one of GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, or GL_UNSIGNED_SHORT_5_6_5_REV and format is not
GL_RGB.

GL_INVALID_OPERATION is generated if height is one of GL_UNSIGNED_SHORT_4_4_4_4,
GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2,
or GL_UNSIGNED_INT_2_10_10_10_REV and format is neither GL_RGBA nor GL_BGRA.